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Multichannel intraluminal impedance (MII) is a validated technique for assessing the movement of fluids, solids, and gas in the oesophagus and is routinely used alongside pH monitoring to characterise gastro-oesophageal reflux (GOR) events. 1 Anaesthesia is known to influence gastric and intestinal motility, potentially predisposing to transient increases in reflux activity.2 Adult studies have demonstrated increased reflux events within minutes of anaesthetic induction and have identified aspiration of gastric contents as a major complication of anaesthesia.3 A small retrospective paediatric study has reported increased GOR parameters, particularly during the first hour and up to six hours post-anaesthesia.4 However, data exploring the impact of anaesthesia on gas reflux in children are lacking. This study aimed to evaluate the effect of general anaesthesia on acid, non-acid, and gas reflux parameters in paediatric 24-hour pH-impedance studies.A retrospective review was undertaken of 100 consecutive 24-hour pH-impedance studies performed between July 2021 and March 2025. Fifty studies were conducted post-anaesthesia (24 following bronchoscopy and 26 following gastroscopy) and fifty without anaesthesia. Studies with a recording duration of less than 20 hours were excluded. Data were extracted from clinician reports for total reflux events, and for acid, weak acid, and non-acid reflux episodes. The number of gas reflux events during the first four hours of recording was quantified using Laborie software. Comparisons were made between the anaesthesia and non-anaesthesia groups using the Mann-Whitney U test, with a p-value of <0.05 considered statistically significant.Analysis demonstrated a significant increase in total gas reflux events in the post-anaesthesia group compared to the non-anaesthesia group (84.17 vs 49.35, p = 0.0039), and in the first four hours of recording (21.36 vs 10.42, p = 0.0030). There was no significant difference in gas reflux between bronchoscopy and gastroscopy subgroups. Acid and non-acid reflux events did not differ significantly between the anaesthesia and non-anaesthesia groups.These findings suggest that general anaesthesia is associated with a significant increase in gas reflux activity in children undergoing 24-hour pH-impedance studies. Gas reflux has been shown to influence symptom association and diagnostic interpretation, as the presence of gas boluses can increase the likelihood of a study being classified as positive for reflux-symptom correlation.5 The observation that gas reflux increases after anaesthesia is relevant, particularly as pH-impedance catheters are frequently placed in theatre to improve tolerance in children. The presence of gas may also reflect aerophagia, which can mimic GER disease and lead to misinterpretation.5A retrospective paediatric study showed increase in acid and non-acid reflux events following anaesthesia for first 4hrs in children over 1yr of age and not in infants.2 This wasn’t seen in our study.While our study benefits from a well-defined cohort and consistent methodology, limitations include its retrospective design, modest sample size, and unaccounted confounding factors such as indication for study, baseline impedance, and premedications. As there are limited small studies, a large prospective study is warranted to confirm these findings and, if validated, adjustments in analysis and interpretation may be required to prevent false-positive results in children undergoing pH-impedance monitoring.References Loots CM, Benninga MA, Davidson GP, Omari TI. Addition of pH monitoring to impedance testing increases the yield of symptom association analysis in children. J Pediatr Gastroenterol Nutr. 2012;54(4):506–512.Omari TI, Rommel N, Staunton E, et al. Effect of anesthesia and sedation on gastroesophageal reflux in children: a prospective study. J Pediatr Gastroenterol Nutr. 2011;53(2):154–158.Reimer C, Bytzer P. Anesthesia and gastroesophageal reflux: implications for aspiration risk. Anesth Analg. 2005;101(3):627–633.Ross JJ, Simpson R, Omari TI. The impact of general anesthesia on gastroesophageal reflux in children undergoing impedance-pH monitoring: a retrospective study. Neurogastroenterol Motil. 2019;31(12):e13723.Wenzl TG, Moroder C, Trachterna M, Thomson M, Silny J. Esophageal pH monitoring and impedance measurement: assessment of reflux in infants and children. Am J Gastroenterol. 2002;97(6):1351–1357.